I have read on the site that micro bubbles are a sign of needed filter maintenance.My fx5 has been running 2 months;can I just rinse the blue filter pad (in TW) or should I also rinse all of the bio-max rings as well.

I have never heard the bubble theory before. You really use your own discretion when it comes to cleaning your filter. I will expect your filter to be quite dirty by now if it hasn't been done for two months. Just to be on the safe side clean all of the media out in existing tank water. You can give the filter pads a really good rinse and get them nice and clean, after all they do most of the work catching all the solid debris. When it comes to your biological filtration, be a little bit more careful, just give it a rinse to remove any solid debris but don't go out of your way to make it sparkling clean.

I get these bubbles every now and then from my 2 xp4's on my Malawi tank, interestingly I never get it from the sunsun...
Any way, after many a rude word, I traced the problem to the intake pipe!

It has a habit of blocking half way in, making the pump suck harder to get in the water, which lowers the water inside the pump, which in turn brings the propellor into contact with the top of the water, and as the propeller spins, its creates bubbles, which are spat out the 'out' pipe!!

It only ever happens with my Malawis, but then the malawis are in a tank with a higher ph, 8.2, and higher ph helps slime algae to grow, and its slime algae that grows inside the intake pipe and blocks it.. I dont know why it only affects the in pipe though, and not the out!!

Anyway I dont know if this helps, but its worth checking.

I agree, my guess would be air in the system somewhere. Check to make sure everything is connected properly, and nothing is getting air, or leaking water!

when you say micro bubbles? do you mean on the heater and things?
usually you get this when you first set your tank up and should settle after a day of two, are you doing to large water changes?
or if you do mean air bubbles then the fx5 turns itself off every 24 hours to expunge air, as above you maybe ready for a media clean by now, again i would think if it was getting heavy in crap it would slow the flow, so the bubbles is a bit of a mystery

I will clean everything carefully in tank water and check out intake connections. I will post results to see if bubbles stop. Maybe it was in the operations manual that I read about the bubbles?

Like torbay said its caused when your pump is having to work extra hard (learned this when I did a TON of canister research). It could be that your sponge filters are too dirty of there is a blockage somewhere but no matter what the cause it giving it a good cleaning will fix it. Also when you do clean it get the impeller spotless because they have a nasty habit of binding up when you try to turn it back on (The main reason Im going to a ehiem Pro III when I get a larger tank).